This invention comprises a method and an apparatus for cleaning with ultrasonic vibratory energy. The invention is especially suitable for cleaning, with ultrasonic vibrations or energy, mass produced parts such as screws, nuts, bolts and similar fasteners, ballbearings, machine parts, parts for instruments, watches and other precision products.
The need for cleaning often exists at the end of a production line to remove fats, oils, dirt, carbon particles, soot, metal particles, oxides, etc. Also, within a production cycle there are needs for cleaning of component parts such as, for instance, those which in a later production step will go through electrolytic surface coating. Different apparatuses on the market at the present time for cleaning of component parts using ultrasonic vibrations or energy are built for a liquid as a medium in which the component parts are immersed during the cleaning. In these apparatuses one utilizes the force that develops at the intermediary surface between a liquid and a solid body when an ultrasonic field is put through the liquid bath. This force is primarily the result of a very high acceleration of the sound at the transition from the liquid to the solid body. Solid body is for this purpose defined not only as the component part which is to be cleaned, but also as the particles of different kinds which are to be removed from the component part. Also, fats, oils and similar substances on the surfaces of component parts cause such acceleration forces. These forces are normally stronger than the forces that exist between the adhering particles and the component parts to be cleaned.
In many liquids there also develops cavitation in addition to the acceleration forces under the influence of an ultrasonic field. Cavitation generates air or gas bubbles at the intermediary surfaces between solid bodies and the liquids. The bubbles are exposed to very high pressures, often 100 times higher than the dynamic pressure of the ultrasonic field. This cavitation plays an important role also in the cleaning of component parts because of its explosion effect. Cavitation, however, is only at hand at relatively low frequencies of the ultrasonic field. It is also enhanced by those liquids which have the ability to dissolve gases. The cavitation effect has one disadvantage, namely that it highly corrodes most materials. This fact puts a limit on the time such component parts which are susceptible to corrosion can be exposed to the cleaning process. This is one of the problems this invention is meant to solve.
In the apparatuses for cleaning of component parts using ultrasonic which are on the market, the component parts to be cleaned are often placed in baskets which are moved through an ultrasonic field. A disadvantage of this method is that parts which are located in the shadow of other parts in the ultrasonic field receive significantly weaker ultrasonic power than those which are directly exposed to the ultrasonic energy. Other types of apparatuses contain a drum of perforated plate in which rotation of the drum tumbles the parts to better expose the parts to the ultrasonic energy. In a third type of apparatus, the parts sink vertically down in a liquid bath and pass through an ultrasonic field. All of these types of apparatuses have in common the fact that the ultrasonic energy reaches the particles to be cleaned from a liquid bath. The loss of ultrasonic energy is substantial in passage through the liquid bath, which means that the ultrasonic energy has to be generated by relatively high energy transducers, and has to be used in combination with long treatment times, in order to achieve the desired degree of cleaning.